WOMEN with a history of endometriosis, a common, often painful condition linked to infertility, have higher rates of three types of ovarian tumour, a large study has found - an insight that could help focus future efforts to detect the often-missed cancer.
Compared with women without a history of endometriosis, those who did suffer from the condition had more than three times the risk of developing clear-cell ovarian cancer, and more than double the risk of endometrioid ovarian cancer.
While previous studies had suggested both these cancers were linked to endometriosis, the new research confirms it, and adds a third type of ovarian cancer linked to the condition, called low-grade serous ovarian cancer, which was twice as common in women with endometriosis than in other women.
Endometriosis is estimated to affect about 6 per cent of Australian women, and as many as 15 per cent of those with chronic abdominal pain. It occurs when the tissues that normally line the uterus start growing on the outer walls of the ovaries, fallopian tubes, bowel and other nearby structures - swelling and bleeding in response to the woman's hormones just as the uterine cells do.

The new research, undertaken by a team from more than 20 international institutions including the Queensland Institute of Medical Research, pooled the results from 13 previous studies, including one from Australia, that jointly covered more than 23,000 women.
The merged analysis found that while 6.2 per cent of 13,226 women without cancer had a history of endometriosis, this shot up to 20.2 per cent of the 674 women with clear-cell ovarian cancer, and 13.9 per cent of the 1220 with the endometrioid variant of the disease.
Endometriosis was also present in 9.2 per cent of the 336 women with low-grade serous subtypes of ovarian cancer.
Reporting the results in the journal The Lancet Oncology, the authors said that although most women with endometriosis did not develop ovarian cancer, doctors should be aware of the increased risks.
Cancer Council Australia CEO Ian Olver said there was currently no screening test for ovarian cancer - which killed an estimated 950 Australian women in 2010 - and the addition of endometriosis as a risk factor for some of the most common types could help narrow down which women a future screening push could usefully focus on.
"It's the next step to say we can identify a high-risk group, and this is one more risk factor to help us do that," Professor Olver said.